Hand-operated controls, such as aircraft control sticks, joysticks, and other manual input devices operated at least in part by hand, collectively referred to herein as “inceptors”, enable a pilot or other operator to provide manual input to control a controlled system, such as an aircraft, a drone or other remote control aircraft, a guided weapon, an electronic game, a robot or robotic arm or other element, heavy equipment, etc. Depending on the design, an operator may provide input by one or more of manipulating a hand grip in one or more directions, such as side-to-side, forward-and-back, and/or twisting about a vertical axis; operating a trigger or other finger-operated input device; and manipulating a thumb-operated input device, such as a thumbwheel, thumb-operated joystick, or button.
In simple mechanical systems, such as older aircraft, a control stick or other inceptor may be linked mechanically to a corresponding control surface of the aircraft. In most modern aircraft, however, control stick inputs cause an electronic output representative of the manual input to be provided. A flight control system may use the electronic output to determine and send control signals to corresponding flight control surfaces and/or motors, referred to collectively herein as “actuators”.
In such electronic control systems, in aircraft and in other applications, a control stick may be equipped with mechanical springs or other structures configured and positioned so as to tend to return the control stick to a center position once the stick is released. In some systems, the springs may be configured to provide a haptic feedback to the operator (e.g., a sense of push back or resistance) so the operator has a sense that the desired input is being provided, including in some cases by giving the operator a sense of a degree to which the input device has been actuated within an available operating range.
Inceptor springs may be subjected to repeated stresses and as a result may fail after a certain number of cycles. Springs may exhibit a non-linear behavior at or near zero displacement, requiring pilots or other operators to apply a “breakout force” to manipulate an inceptor from the zero or “center” position, which some pilots may not find to be desirable.